Alcatel N.v.

Alcatel Alsthom Compagnie Generale D'electricite

Alcatel Sel Aktiengesellschaft

Alcatel

Henning Bulow

Rolf Heidemann

Thomas Pfeiffer

Heinz G Krimmel

Jurgen Otterbach

Gustav Veith

Rolf Rossberg

An electrical equalizing facility for an electric input signal (S) which was derived from an optical signal (L) transmitted over an optical fiber and which is distorted due to interference in the optical signal (L) as a result of, e.g., polarization mode dispersion (PMD) comprises a number (n&gt;1) of parallel-connected, different, variable electronic equalizers (E.sub.1, . . . , E.sub.i, . . . E.sub.i,m), which are supplied with the electric input signal (S), and a control unit (3) for selecting the electric output signal (S.sub.i) of the respective best equalizing electronic equalizer (E.sub.i) and for controlling the equalization parameters (E.sub.i,1, . . . , E.sub.i,m) of this equalizer in such a way that the quality (Q) of its equalized signal (S.sub.i) is optimized. This makes it possible to select the equalizer currently operating satisfactorily.

Method and facility for equalizing an electric signal distorted due to

A wavelength converter is disclosed having a Sagnac interferometer (NOLM, nonlinear optical loop mirror) as its essential part. In order that the wavelength converter can also be used for NRZ (nonreturn-to-zero) signals, it has a 3.times.3 coupler (2) with six ports (6-11).

Wavelength converter suitable for high bit rates

An optical receiver is presented, which can receive and evaluate an optical signal (S) containing interference caused by polarization mode dispersion (PMD). The optical receiver has a splitting facility (1.1) which splits the routable optical signal (S) into two electrical signal components (S.sub.-, S.sub.+). The electrical signal components (S.sub.-, S.sub.+) are processed in an equalizing circuit (1.2). A control facility (1.3) controls the splitting facility (1.1) with the aid of a quality signal (Q) produced by the equalizing circuit (1.2).

Optical receiver with an equalizing circuit for PMD-induced

A demultiplexing apparatus is disclosed which comprises a pulse generator (4), a phase control device (3), and an optical switching device (1), e.g., a NOLM. The phase control device (3) controls the pulse generator (4), whose pulse initiates switching operations in the optical switching device (1) depending on the magnitude of an electric signal derived from the output (8) of the optical switching device (1). The phase control device (3) includes a noise source (26) which disturbs the pulse in a defined manner.

Apparatus for demultiplexing an optical digital signal

It is necessary to know the zero dispersion wavelength .lambda..sub.0, to ensure the reliable transmission of high bit-rate frequency signals via remote transmission paths. The method for determining the zero dispersion wavelength of an optical waveguide knowingly utilizes a disturbing effect that is undesirable in optical communications transmission techniques, which is able to lower the transmission quality. This effect is the so-called four-wave mixing, or in special cases a partially degenerated four-wave mixing. The method couples two light signals of different wavelengths (.lambda..sub.1, .lambda..sub.2) into an optical waveguide (4). A mixing product which occurs in the optical waveguide as a result of a partially degenerated four-wave mixing is evaluated by an analyzer (3). The wavelength of one of the two light signals is selectively varied until the optical output of the mixing product reaches a maximum. At that point the wavelength of this light signal coincides with the zero dispersion wavelength .lambda..sub.0.

Method of determining the zero dispersion wavelength of an optical

A laser (2) of an optical transmitter (1) for the transmission of an analog broadband signal for CATV in particular, can be amplitude-modulated in two different manners with an intelligence signal (N). Direct modulation can lead to an undesired additional frequency modulation. With indirect modulation by means of an optical intensity modulator (3), Brillouin scattering occurs at powers of approximately 10 mW in an optical fiber of the transmission path connected to the optical transmitter (1). Both modulations lead to distortions of the transmitted signal. In order to avoid the disadvantages of both modulations in a technically simple fashion, the carrier emitted from a laser (2) is indirectly modulated with an intelligence signal (N) and the laser (2) also faintly directly modulated with an energy-dispersing signal (V). The faint direct modulation leads to a constant, limited wave length alteration of the optical signal, such that Brillouin scattering is reduced, simultaneously with the avoidance of dispersion distortions.

Optical transmitter

The optical mixer (1) contains a polarization-maintaining length of optical waveguide (4) as a mixing element. The pump light (P) is coupled to the optical mixer in so that its plane of polarization makes an angle of 45.degree. with the principal axes of the length of optical waveguide (4). One advantage of this optical mixer (1) is that the optical power of the mixing product (M) depends not on the polarization of the signal light (S), but only on the phase relationship between signal light and pump light. The mixer can be used to advantage in an optical phase-locked loop.

Optical mixer and its use

An optical transmitter for the joint transmission of analog and digital signals is indicated, which, although it contains an optical transmitting component (5) with a laser, does not exhibit an increase in the bit error rate when transmitting the digital signals, due to so-called clipping. The clipping, a negative overmodulation of the laser to below the laser threshold, which occurs because of the constructive interference of the analog signal carders, is prevented by a limiter (8) located upstream of the modulation input of the optical transmitting component (5). The limiter contains a time-variant network that supplies a specified minimum voltage to the modulation input every time a comparator (7) determines that the modulation voltage has dropped below the predetermined threshold.

Optical transmitter for the common transmission of analog signals and

An optical system includes a fiber-optic amplifier having a section of optical waveguide doped with a rare-earth element and a pump-light source for emitting pump light, the fiber-optic amplifier receiving signal light of a first wavelength and outputting at least signal light of a second wavelength. An optical-to-electrical transducer receives the signal light of the second wavelength from the fiber-optic amplifier and produces an electrical output signal. The signal light of the second wavelength is pump light which is unabsorbed in the section of optical waveguide.

Fiber-optic amplifier as wavelength converter

In fiber-optic amplifiers, various parameters, such as the input power, are measured to obtain information on the operating condition of the transmission link and of the fiber-optic amplifier itself. In prior art fiber-optic amplifiers, a portion of the input power is coupled out for this purpose by means of a coupler (2). If low-power optical signals such as digital signals are transmitted, the coupled-out portion of the input power can only be detected with complicated and costly circuitry. In the novel fiber-optic amplifier, the pump power and input power are monitored by coupling out and evaluating the radiation resulting from amplified spontaneous emission (ASE). This provides information on the state of the input signal.

Fiber-optic amplifier with a facility for monitoring the pump power and

For so-called add-drop multiplexers, fast optical switches (SCH) are needed which can switch optical signal waves stemming from different signal sources. Known optical switches include an interferometer in which the signal wave is split into two signals, and in which an optical switching pulse is superimposed on one of the signals. Because of the Kerr effect, interference signals can be generated which can be switched in an optical coupler in a controllable manner to a predetermined output. The signals and the switching pulse have the same direction of polarization, which may cause switching problems with signals from different signal sources. The gist of the invention therefore lies in the use of switching pulses which consist of quasi-depolarized light. Such switching pulses are advantageously generated in two switching-pulse sources (SQ) in which two polarized light beams are superimposed orthogonally. In an optical waveguide (LWL.sub.1, SP) with a nonlinear refractive index, the switching pulse assumes a constantly varying polarization state.

Interferometric optical switch

To increase the pump efficiency in a fiber-optic amplifier, the pump coupler (2) is fabricated from a fiber whose mode field diameter for the pump light is adapted to the mode field diameter of the active length of fiber (7). In an alternative solution, the arm of the pump coupler (2) coupled to the pump source (1) on the one hand and connected to the active length of fiber (7) on the other hand consists of a fiber adapted to the mode field diameter of the active length of fiber (7), and the arm of the pump coupler (2) serving as a connection to the incoming transmission line (8) consists of a fiber corresponding to the optical waveguide of the transmission line (8).

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Stuttgart, Germany

Henning Bulow